1. Field of the Invention
The present invention relates to a method and apparatus for carrier management, and more particularly, to a method and apparatus for performing carrier management in a user equipment (UE) of a wireless communication system to support carrier aggregation.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
However, the 3rd Generation Partnership Project (3GPP) has started to work out a next generation of the LTE system: the LTE Advanced (LTE-A) system, to meet future requirements of all kinds of communication services. Carrier Aggregation (CA) is introduced in the LTE-A system, which enables the UE to aggregate multiple carries for transmission, such that the transmission bandwidth and spectrum efficiency can be enhanced.
At present, the characteristics of carrier aggregation are quoted as below:
(1) Supporting carrier aggregation for both contiguous and non-contiguous component carriers.
(2) The aggregated number of component carriers in the uplink (UL) and the downlink (DL) can be different. For backward-compatible configuration, the aggregated numbers of component carriers in the UL and the DL should be the same.
(3) It is possible to configure a UE to aggregate a different number of component carriers in the UL and the DL to obtain different bandwidths.
(4) From a UE perspective, there is one transport block and one hybrid-ARQ (HARQ) entity per scheduled component carrier. Each transport block is mapped to a single component carrier only.
Besides, carrier configuration for Carrier Aggregation can be done through Radio Resource Control (RRC) Reconfiguration. For example, the network may send an RRC Connection Setup message or a RRC Reconfiguration message to configure component carriers of the UE.
Generally, after having Carrier Aggregation, the UE may have to monitor several carriers configured by upper layers (e.g. RRC layer) simultaneously, to obtain related control and scheduling information of the configured carriers, such that data reception can be each performed on the configured carriers. However, in some conditions (e.g. low data rate, or in UE idle state), some carriers are not used. Keeping monitoring all the configured carriers would cause unnecessary power consumption of the UE. Thus, some of the configured carriers have to be turned off or deactivated correspondingly. As mentioned above, the carrier configuration is done though higher layer signaling, and thus cannot respond quickly to the changed condition of the UE.